The 22-year-old (pictured with manager Craig Elliott and fellow new signing Ben Davies), who will not be eligible to face Spennymoor Town on Saturday due to serving the final match of an existing suspension, could make his United debut at Bradford Park Avenue on Bank Holiday Monday.
Keane, capable of playing in defence or midfield and the brother of former United defender Jordan, has linked up with the Pilgrims after leaving Alfreton Town on the eve of the season — having also appeared in National League North for Worcester City and Kidderminster Harriers.